The present invention generally relates to medical device catheters, as well as to processes for making same. More particularly, the invention relates to medical devices in the form of catheters that exhibit varying flexibility along the length of the catheter shaft while simultaneously exhibiting high pressure capabilities throughout the length of the catheter. A portion of the catheter shaft which is positioned generally distally therealong is particularly thin-walled and flexible when compared with the rest of the catheter shaft. This thin-walled and flexible component has an exceptionally high burst strength and is prepared by a procedure which includes radially expanding a parison. Exemplary catheters include so-called balloon catheters such as those designed for angioplasty, valvuloplasty, urological uses and the like.
Various types of catheters are used for different types of medical applications. In several instances, the catheters must wind their way through curved and/or branched body passageways or vessels, necessitating a catheter body that is flexible while still exhibiting adequate stiffness to supply torque properties which enable the catheter to be fed and maneuvered without kinking or excessive twisting which will hamper proper movement through the body cavity or vessel. At the same time, flexibility, particularly at the distal end or lead portion of the catheter should be provided in order to present bending attributes whereby the distal portion of the catheter can be more easily guided into branching passageways or more readily follow tortuous pathways of body vessels or cavities. Numerous approaches have been taken in attempting to achieve the desired combination of adequate torque and flexibility. Some include the addition of mechanical components such as coiled wires. Others seek to provide polymers which exhibit a compromise between competing desired attributes, at times in connection with specific types of catheters. Still other approaches incorporate treatments of catheter bodies or shafts in an effort to provide desired properties.
Some of these approaches are not particularly suitable when the body passageway is especially narrow and/or when the catheter body or shaft must provide a threshold burst strength which is needed for delivering fluids through the catheter body or shaft. Typical medical device catheters of this type require both thinness and exceptional wall strength while still being maneuverable through narrow, curved pathways or branches. These types of catheters include those which must pass through narrow, branched blood vessels in order to deliver pressurized fluid to a location within the body. A particular type of catheter in this regard delivers pressurized fluid to a balloon component at a distal portion of the catheter. Balloon components of this type, when filled with the pressurized fluid will distend or increase in radial size, typically in order to compact or reduce the size of a lesion which has developed in a diseased body cavity such as a blood vessel. An exemplary procedure in this regard is known as percutaneous transluminal coronary angioplasty, and catheters especially designed to carry out this procedure are known as percutaneous transluminal coronary angioplasty (PTCA) catheters.
The typical PTCA catheter utilizes an outer body or shaft having a single flexibility designed to provide a compromise in performance characteristics. The compromise involves a target flexibility that provides some aspects, but not necessarily the ideal aspects, of having a distal end which is flexible to conform to the anatomy while being stiff enough in the proximal end to be pushable, and at the same time being able to withstand the required fluid pressures to inflate the balloon. By proceeding in accordance with the present invention, there is no need to attempt to attain these compromises. The proximal shaft of an outer catheter assembly is as stiff as desired for maximum pushability and strength, while a distal section which is particularly thin and flexible imparts minimal stiffness and exceptional strength to the distal portion of the outer catheter assembly. In the preferred embodiment, stiffness of this distal portion is controlled by an inner tube or shaft which is coaxial with the outer catheter assembly.
In summary, the medical device catheter has a shaft or catheter body composed of an elongated tube having a selected, relatively great stiffness. A thin-walled flexible tube is secured to the distal end of the elongated, stiff catheter body. This thin-walled flexible tube has a stiffness substantially less than that of the elongated catheter body, and its thin-walled and flexible characteristics preferably are developed, at least in part, by a procedure wherein the thin-walled, flexible tube is made from a parison that is radially expanded. In the preferred embodiment, this thin-walled flexible tube connects the distal end of the elongated, stiff catheter body with a tip member such as the proximal end portion of a medical device balloon having a non-distended, collapsed profile which expands to a distended profile upon the application of high fluid pressure through the elongated catheter, including the thin-walled flexible tube, which although being exceptionally flexible is also exceptionally high in burst strength so as to be adequate to withstand the high pressure of the fluid therewithin.
It is a general object of the present invention to provide an improved medical device catheter having multiple flexibilities along its shaft while simultaneously exhibiting high pressure capabilities.
Another object of this invention is to provide an improved percutaneous transluminal coronary angioplasty catheter that is especially well-suited to follow bends and branches within blood vessels and the like while still possessing burst strength adequate to withstand the high pressures needed for angioplasty procedures.
Another object of the present invention is to provide an improved outer tube assembly for coaxial catheters, which outer tube assembly exhibits multiple flexibilities including minimal flexibility at a distal portion location whereby distal stiffness is controlled by the inner, coaxial tube.
Another object of this invention is to provide an improved coaxial catheter having an inner tube or body which accommodates a guidewire and provides distal stiffness to the outer coaxial tube having a unique section of minimal stiffness and maximum flexibility.
Another object of this invention is to provide an improved catheter having a distal portion section which is of minimal stiffness and of high burst strength by preparing same from a parison that is radially expanded.
Another object of the present invention is provide an improved medical device balloon catheter incorporating a section of minimal stiffness and maximum flexibility in order to provide a balloon catheter having a portion immediately proximal to the balloon which allows the balloon to easily follows bends and branches within body cavities or vessels.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the detailed description.